Experimental evidence that group foragers can converge on predicted producer-scrounger equilibria

Abstract

When foraging together, animals are often observed to feed from food discoveries of others. The producer-scrounger game predicts how frequently this phenomenon of food parasitism should occur. The game has two major requirements: (i) all individuals must either produce, meaning they invest time and/or energy getting resources, or scrounge, meaning they try to get resources from producers, and (ii) the payoffs received from the scrounger tactic must be highly negatively frequency-dependent such that they do better than producers when rare, but worse when common. This study provides the first experimental support for the use of the producer-scrounger game in group foraging contexts. A total of five flocks of spice finches (Lonchura punctulata) were used on two experiments. Payoffs were measured by feeding rate (seeds/s) in two feeding conditions. In all cases, payoffs to scroungers were found to be highly negatively frequency-dependent on the frequency of scrounging. All functions were linear (p $<$.05). In the second part of experiment 2, birds adopted the predicted producer or scrounger foraging tactics over a series of trials lasting 16 days (eight consecutive per feeding condition). In both experiments, individuals in the flocks also demonstrated plasticity in tactic used. Future studies should look at testing the performance of different learning rules using a similar experimental design.